Attrition mill



49. w. D. slLcox 237mg ATTRITION MILL juiy 2,

Filed June 5 1945 IN VEN TOR.

Patented July 26, 1949 ATTRITION William D. Silcox, Lewistown, Pa., or to American Viscose Corporation,

Wilmington,

Del., a corporation of Delaware Application June 5, 1945, Serial No. 597,704

Claims.

This invention relates to a device for reducing the size of solid masses suspended in liquids, such as a slurry of cellulose xanthate crumbs in water or an alkaline solution, to facilitate the dispersion or dissolution of the solid material.

In accordance with the present invention, a device is provided which has a plurality of stages of attrition separated by intermediate redistribution chambers in which the particles are more homogeneously distributed in the liquid by agitating means before further attrition is performed thereon. A cutter is also advantageously arranged to operate upon the slurry even before it enters the attrition devices and advantageously, the agitating means positioned intermediate the stages of the device take the form of impellers which are so arranged as to force the slurry into the next stage of size reduction means. Ad- :iitional objects, features and advantages of the invention will be apparent from the drawing and the following description thereof.

In the drawing-- Figure 1 is a cross-sectional elevation of a preferred embodiment of the invention;

Figure 2 is a cuss-sectional elevation of the stator with the rotor removed; and

Figure 3 is an elevation of the rotor.

The device comprises a generally tapered rotor 2 driven by the shaft 3 by suitable means therebelow not shown. The rotor operates within a casing 4 which is split longitudinally and may be hingedly mounted at one side to facilitate inspection, cleaning, and repair. Adjacent the narrow top of the rotor, it is provided with a plurality of annular rows of teeth 5 which interrnesh between annular rows of teeth 6 which extend radiallyinwardly from the stationary casing or stator 4. Except for the fact'that the teeth 5 and B extend radially and are arranged in annular rows which interfit, the precise shape of the teeth and the precise manner of distribution within a given annulus is not critical, but may take the forms and arrangements heretofore conventional in similar cutting devices. Below the cutting stage there is provided a plurality of attrition stages with intervening annular mixing chambers. Each attrition stage (four being specifically shown) comprises an annular shoe I :arried upon a cylindrical surface formed upon the rotor and a. similar shoe 8 carried within a cylindrical surface formed within the casing 6. Each shoe i has a plurality of annular ridges which interfit with a predetermined clearance within complementary annular ridges on the internal surfaces of a corresponding shoe 8. The

.rotor just beyond the last attrition stage.

transverse cross-section of the ridges is not critical, but some form of serration is preferred in order to impart a directional component to a slurry passing through the attrition stage in favor of its motion to the discharge end of the device. The peaks of the serrations may be sharp as shown or blunt.

The diameter of the space between the ridges or serrations in each successive stage becomes larger, in order to compensate for a reduced clearance between the serrations in successive stages of attrition. For example, the clearance in the first stage may be about of an inch, whereas that in each succeeding stage is less than the one immediately preceding it, until the fourth stage of attrition may have a clearance of about to of an inch. These clearances are merely representative and may vary, depending upon the particular material which the device is to handle in any particular installation. Between the cutting device and the first stage of attrition, as

well as between the succeeding stages of attrition, an annular mixing chamber 9 is provided in the casing, while the rotor is provided with the agitating blades which are curved as more clearly shown in Figure 2, so that rotation of the rotor causes the blades to act'as impellers tendin to force the slurry into the next stage of attrition. The shaft 3 of the rotor may be provided with impeller blades ii within the coupling l2 which serves as the entrance to the device and, if desired, impeller blades may be provided upon the An annular discharge conduit i3 may be provided between the casing 4 and the rotor 2. If desired, this conduit may take the form of a volute and at one point of its periphery, at the largest diameter in the case of a vclute-shaped conduit, it communicates with the discharge connection i i.

A jacket It for introduction of a cooling medium, such as cold water or brine, or in special cases, a heating medium, such as steam is provided about the stator and a temperature-controlling medium may also be introduced through the shaft which may be hollowed out for this p.-

The device finds its greatest utility in preliminarily breaking down aggregate particles or clumps of particulate material while carried within a slurry within which it is desired to disperse or dissolve the material. For example, in preparing solutions of viscose for spinning filaments, casting films, or producing other shaped articles, the upper coupling 12 may be connected by a suitable conduit to one or more xanthating vessels and the discharge conduit 14 may be connected to one or more dissolving vessels. The xanthate produced in the xanthating vessels is generally in the form of a crumb-like mass, sometimes with the crumbs bunched up into lumps. Preliminary to passing through the cutting and attrition device of the present invention an aqueous medium, such as water itself or an alkaline solution, may be introduced into the xanthating vessel, the agitating means therein suspending the xanthate crumbs loosely within the slurry. After brief mixing in the xanthating vessel, the slurry is discharged therefrom and enters the device through the coupling I2, where the impeller blades I I tend to assist the gravity flow and to direct the material away from the shaft into the annular passage opening into the teeth of the cutter. The cutter reduces any lumps to small size crumbs and from it the slurry passes into the mixing chamber 9, in which re-distribution of the crumbs within the liquid occurs and the impellers force the material into the first stage of attrition. Because of the progressively narrowed clearances between annular serrations in each succeeding attrition stage, the particles in the slurry are progressively reduced in size. At the same time re-distribution within the slurry occurs in each chamber before it passes into the next attrition stage of smaller clearance, thus preventing any tendency for the particles to adhere to the annular serrations and. clog the clearances between them. It is apparently the re-distributing action within the intermediate mixing chambers that prevents the solid materials from accumulating in suflicient concentrations to produce clogging between the annular serrations. This function of the re-distribution is particularly important in the handling of cellulose xanthate because of the adheslveness of the particles. However, other materials of an adhesive pasty nature may also be as advantageously handled by the device of the present invention.

It is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. A device for reducing the size of solid masses suspended in a slurry comprising a stationary member having a plurality of stages each comprising a plurality of annular serrations, each serration extending completely around the interior of the member, a rotor within the stator having a plurality of stages comprising a plurality of annular serrations, each surrounding therotor, the serrations on the rotor interfitting with the serrations on the stator and having a predetermined clearance therefrom, an annular mixing chamber between the stator and rotor and between each two adjacent stages of attrition, and agitation means carried by the rotor within each mixing chamber, at least one stage of cutting means spaced axially from the attrition stages, said stage of cutting means comprising a plurality of annular rows of radially projecting teeth upon the rotor extending between a plurality of annular rows of radially extending teeth within the stator.

2. A device for reducing the size of solid masses suspended in a slurry comprising a stationary member having a plurality of stages each comprising a plurality of annular serrations, each serration extending completely around the interior of the member, a rotor Within the stator having a plurality of stages comprising a plurality of annular serrations, each surrounding the rotor, the serrations on the rotor, interfltting with the serrations on the stator and having a predetermined clearance therefrom, an annular mixing chamber between the stator and rotor and between each two adjacent stages of attrition, and agitation means carried by the rotor within each mixing chamber, at least one stage of cutting means spaced axially from the attrition stages, said stage of cutting means comprising a plurality of annular rows of radially projecting teeth upon the rotor extending between a plurality of annular rows of radially extending teeth within the stator, the stator and rotor being tapered with the cutting means ar ranged at the small diameter ends thereof and the attrition stages between the cutting means and the large diameter ends thereof.

3. A device for reducing the size of solid masses suspended in a slurry comprising a stationary member having a plurality of stages each comprising a plurality of annular serrations, each serration extending completely around the interi or of the member, a rotor within the stator having a plurality of stages comprising a plurality of annular serrations, each surrounding the rotor, the serrations on the rotor interfitting with the serrations on the stator and having a predetermined clearance therefrom, an annular mixing chamber between the stator and rotor and between each two adjacent stages of attrition, and agitation means carried by the rotor within each mixing chamber, at least one stage of cutting means spaced axially from the attrition stages, said stage of cutting means comprising a plurality of annular rows of radially projecting teeth upon the rotor extending between a plurality of annular rows of radially extending teeth within the stator, the stator and rotor being tapered with the cutting means arranged at the small diameter ends thereof and the attrition stages between the cutting means and the large diameter ends thereof, the devices being mounted with the rotor upon a vertical axis of rotation and the small ends of the rotor and stator above the large ends thereof.

a. A device for reducing the size of solid masses suspended in a. slurry comprising a hollow stationary member, a plurality of annular ridged. shoes spaced apart axially inside the stationary member, a rotor within the stator, a plurality of annular ridged shoes carried on the rotor with its ridges interfitting with the ridges on the stator and spaced with a predetermined clearance therefrom, an annular mixing chamber between the stator and rotor and between each two adjacent stages of attrition, and agitation means carried by the rotor within each mixing chamber.

5. A device for reducing the size of solid masses suspended in slurries comprising a stator having a generally tapered interior, a rotor disposed Within the stator and having a corresponding taper, a plurality of stages of attrition spaced enerally axially between the rotor and the stator, each stage comprising a plurality of annular serrated shoes carried on the rotor interfitting with a plurality of annular serrated shoes carried on the stator, with the clearance between the teeth in each stage smaller than that of the immediately preceding stage and the outer diameter of the clearance in each stage larger than the outer diameter of the clearance in the immediately preceding stage, annular mixing chambers between the stator and the rotor and between each two attrition stages, and impellers carried by the rotor in each annular chamber. each annular chamber having its average diameter greater than that of the one immediately precedins.

WILLIAM D. SILCOX. 5

REFERENCES CITED The following references are of record in the file of this patent; 10

UNITED STATES PATENTS Number Name Date Re. 8,845 Taylor Aug. 12, 1879 9,859 Munson July 19, 1853 117,973 Bovey Aug. 15, 1871 15 190,182

Barber May 1, 1877 Number Number Name 9 Date Day Jan. 10, 1899 Kinder May 26, 1903 Bllchfeldt Dec. 28, 1915 Teague Apr; 12, 1927 Soherbaum Dec. 20, 1927 Phillipp Oct. 16, 1928 Fraser Dec. 18, 1928 Acree Nov. 13, 1934 Lord June 16, 1936 Ambrose Mar. 31, 1942 FOREIGN PATENTS Country Date Great Britain July 11, 1919 Germany May 3, 1884 

